Conventionally, as a method of automatically correcting a tone of an image, there has been a method in which a brightness level of an image is corrected for each of pixels included in the image. An example of such method is described in JP-A-9-065252 (counterpart U.S. Pat. No. 5,808,697). In the method, an input image is divided into a plurality of block regions, and an average brightness level (an average of brightness levels of all pixels) is obtained for each of the block regions. Next, a correction curve is independently selected for each of the block regions corresponding to the average brightness level. Next, a plurality of types of correction curves selected for a block region (a main block region) including a target pixel and for a plurality of block regions (subsidiary block regions) which are adjacent to the main block region are subjected to a weighted average to generate a new correction curve, and the new correction curve is used to correct the brightness level of the target pixel. According to the method described above, it is possible to prevent the details of a local portion in the image from being lost by performing a tone correction on the image.
According to the conventional method, it is possible to prevent the details of the local portion from being lost with the tone correction. However, the conventional tone correction is designed for a general-purpose use, and its effect may be limited in some cases. For example, in a case in which a human face exists in an image to be subjected to the tone correction, a contrast between a bright portion and a dark portion in the face portion tends to be deteriorated, and when a brightness of a face portion, where the human face is positioned, and a brightness of background portion largely differ from each other, the face portion becomes unnaturally bright or dark by the tone correction. As described above, the conventional tone correction may not apply a favorable correction to the face portion.